Catalyst system containing an autoacceleration inhibitor

ABSTRACT

In a transition metal catalyst system, the improvement comprising including in the catalyst system an autoacceleration inhibitor, which (i) at about the temperature at which the catalyst system autoaccelerates, decomposes into a poison for the catalyst system; (ii) is present in the catalyst system in an amount sufficient to provide the quantity of poison required to inhibit the autoacceleration of the catalyst system at the autoacceleration temperature; and (iii) is either essentially inert at the normal operating temperature of the catalyst system or will cause substantially less inhibition of the catalyst system at the normal operating temperature than at the autoacceleration temperature.

TECHNICAL FIELD

This invention relates to a catalyst system containing anautoacceleration inhibitor.

BACKGROUND ART

Paradoxically, the high activity at elevated temperatures, which makesmany transition metal catalyst systems so attractive, is alsoresponsible for a negative characteristic. This deficiency exhibitsitself in the form of a kinetic profile, which can be described as"autoacceleration", and leads to processes, which are, in effect, out ofcontrol; processes in which the reactants are "over reactive";agglomeration of particulate product; and other various undesirableresults such as hot spotting, chunking, and sheeting.

Autoacceleration can be defined as an abrupt increase in the reactionrate of a process to an undesirable level due to a sudden rise intemperature. In effect, the system is unable to remove the heat as fastas it is generated. Control of this behavior is essential for the smoothoperation of the process in the reactor. The usual response to a reactorupset caused by autoacceleration is to have the operator initiate areactor kill by the rapid injection of a catalyst poison. The initiationof such a drastic measure is made at the discretion of the operator, anddepends entirely on his judgment as to the performance of the catalystin the reactor.

To relieve the operator of the responsibility for making this decision,which, at least in part, tends to be subjective, in-situ control ofcatalyst kinetics has been suggested, the goal being to let the catalystmonitor its own behavior.

DISCLOSURE OF THE INVENTION

An object of the invention, therefore, is to provide a catalyst system,which will, in-situ, essentially avoid autoacceleration. Other objectsand advantages will become apparent hereinafter.

According to the present invention, an improvement in a transition metalcatalyst system has been discovered, which meets the above objective.The improvement comprises including in the catalyst system anautoacceleration inhibitor, which (i) in the temperature range at whichthe catalyst system autoaccelerates, decomposes into a poison for thecatalyst system; (ii) is present in the catalyst system in an amountsufficient to provide the quantity of poison required to inhibit thecatalyst system in the autoacceleration temperature range; and (iii) iseither essentially inert in the normal operating temperature range ofthe catalyst system or will cause substantially less inhibition of thecatalyst system in the normal operating temperature range than in theautoacceleration temperature range.

DETAILED DESCRIPTION

Subject invention is considered to be universal in that theautoaccelaration inhibitor can be used advantageously in any transitionmetal catalyst system employed in a process in which auto-accelerationis a potential problem.

Examples of various catalyst systems and autoacceleration inhibitorstherefor are set forth in Table I. It will be understood thatautoacceleration and decomposition temperature ranges vary from systemto system and inhibitor to inhibitor. Those mentioned in Table I providesome guidance for the particular catalyst systems mentioned.

                                      TABLE I                                     __________________________________________________________________________                                                        Decomposition                                                                 Temperature of                         Process In Which The Catalyst                                                                 Autoacceleration                                                                       Autoacceleration                                                                            Autoacceleration          Catalyst System                                                                            System Is Utilized                                                                            Temperature (°C.)                                                               Inhibitor     Inhibitor                 __________________________________________________________________________                                                        (°C.)                e.g., VCl.sub.3 /AlR.sub.3 and                                                           Olefin Polymerization, e.g.,                                                                  About 110 to 125                                                                       Metal Carbonyls,                                                                            About 110 to 130            TiCl.sub.3 /MgCl.sub.2 /AlR.sub.3                                                        see U.S. Pat. Nos. 4,302,566                                                                           Dicyclopentadiene,                                   and 4,508,842            Sulfones                                  (R.sub.3 P).sub.2 Rh(H)(CO)                                                              Olefin Hydroformylation, e.g.,                                                                >100     Dicylopentadiene,                                                                           100 to 130                  (supported liquid                                                                        see U.S. Pat. No. 3,487,112.                                                                           Sulfones                                  phase catalyst)                                                                          Also see J. Mol. Catal. 1985                                                  vol. 31, page 107.                                                 Ni Catalysts, i.e.,                                                                      Olefin Oligomerization, e.g., see U.S. Pat. No.                                               about 100                                                                              Dicylopentadiene, Sulfones                                                                  100 to 130                   ##STR1##                                                                     Pd/Al.sub.2 O.sub.3                                                                      Hydrogenation of Polyenes                                                                     >150                                                                                    ##STR2##     >150                        PdCl.sub.2 /CuCl.sub.2                                                                   Wacker Process (Olefins to aldehydes and ketones)                                             >130                                                                                    ##STR3##     >130                      __________________________________________________________________________

The invention will be discussed in terms of a typical catalyst systemuseful in the polymerization of alpha-olefins, particularly for theproduction of homopolymers and copolymers of ethylene, i.e., a vanadiumcatalyst system comprising:

(i) the reaction product of a vanadium compound and an electron donor,which is a liquid, organic Lewis base in which the vanadium compound issoluble;

(ii) a silica support into which component (i) is impregnated;

(iii) a halocarbon promoter;

(iv) a hydrocarbyl aluminum cocatalyst; and

(v) as an autoacceleration inhibitor, a Diels-Alder adduct or atransition metal carbonyl,

with the proviso that the inhibitor is such that it will decompose whenthe catalyst system reaches its autoacceleration temperature range.

It will be understood that some inhibitors will be essentially inert inthe normal operating temperature range while others will decompose inthe normal operating temperature range, but will cause substantiallyless inhibition of the catalyst system in the normal operatingtemperature range than in the autoacceleration temperature range.

The vanadium compound can be any one of the well known group of vanadiumcompounds used to form those complexes, which find use as catalystprecursors in polymerization processes. Examples are vanadiumtrihalides, vanadium tetrahalides, and vanadium oxyhalides. The halidesare generally chlorides, bromides, or iodides, or mixtures thereof. Ofthese compounds VCl₃, VCl₄, and VOCl₃ can be mentioned. The vanadiumacetylacetonates such as vanadyl triacetylacetonate are also useful.

The electron donor is a liquid, organic Lewis base in which the vanadiumcompound is soluble. It can be selected from the group consisting ofalkyl esters of aliphatic and aromatic carboxylic acids, aliphaticketones, aliphatic amines, aliphatic alcohols, alkyl and cycloalkylethers, and mixtures thereof, each electron donor having 2 to 20 carbonatoms. Among these electron donors, the preferred are alkyl andcycloalkyl ethers having 2 to 20 carbon atoms; dialkyl, diaryl, andalkylaryl ketones having 3 to 20 carbon atoms; and alkyl, alkoxy, andalkylalkoxy esters of alkyl and aryl carboxylic acids having 2 to 20carbon atoms. The most preferred electron donor is tetrahydrofuran.Other examples of suitable electron donors are methyl formate, ethylacetate, butyl acetate, ethyl ether, dioxane, di-n-propyl ether, dibutylether, ethyl formate, methyl acetate, ethyl anisate, ethylene carbonate,tetrahydropyran, and ethyl propionate.

While an excess of electron donor is used initially to provide thereaction product of vanadium compound and electron donor, the reactionproduct finally contains about 1 to about 20 moles of electron donor permole of vanadium compound and preferably about 1 to about 10 moles ofelectron donor per mole of vanadium compound. About 3 moles of electrondonor per mole of vanadium compound has been found to be mostpreferable.

The silica support is a solid, particulate porous material essentiallyinert to the polymerization. It is used as a dry powder having anaverage particle size of about 10 to about 250 microns and preferablyabout 30 to about 100 microns; a surface area of at least about 3 squaremeters per gram and preferably about 50 square meters per gram; and apore size of at least about 80 angstroms and preferably at least about100 angstroms. Generally, the amount of support used is that which willprovide about 0.05 to about 0.6 millimole of vanadium compound per gramof support and preferably about 0.3 to about 0.5 millimole of vanadiumcompound per gram of support.

The halocarbon promoter can have the following formula:

    R.sub.a CX.sub.(4-a)

wherein

R=hydrogen or an unsubstituted or halogen substituted alkyl radicalhaving 1 to 6 carbon atoms;

X=a halogen; and

a=0, 1, or 2.

The halogen can be chlorine, bromine, iodine, or fluorine, and each Xcan be alike or different. Preferred promoters include fluoro-, chloro-, and bromo-substituted methane or ethane having at least 2 halogenatoms attached to a carbon atom, e.g., chloroform, CFCl₃, CH₃ CCl₃,carbon tetrachloride, and CF₂ ClCCl₃. The first three mentionedpromoters are preferred. About 0.1 to about 10 moles, and preferablyabout 0.2 to about 2 moles, of promoter can be used per mole ofcocatalyst.

The hydrocarbyl aluminum cocatalyst can be represented by the formula R₃Al wherein each R is an alkyl radical; each R can be alike or different;and each R has 1 to 14 carbon atoms, and preferably 2 to 8 carbon atoms.Further, each alkyl radical can be a straight or branched chain.Examples of suitable radicals are: methyl, ethyl, propyl, isopropyl,butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, 2-methylpentyl,heptyl, octyl, isooctyl, 2-ethylhexyl, 5,5-dimethylhexyl, nonyl, decyl,isodecyl, undecyl, and dodecyl.

Examples of suitable hydrocarbyl aluminum compounds are as follows:triisobutylaluminum, trihexylaluminum, di-isobutylhexylaluminum,isobutyl dihexylaluminum, trimethylaluminum, triethylaluminum,tripropylaluminum, triisopropylaluminum, tri-n-butylaluminum,trioctyaluminum, tridecylaluminum, tridodecylaluminum,tribenzylaluminum, triphenylaluminum, trinaphthylaluminum, andtritolylaluminum. The preferred hydrocarbyl aluminums, aretriethylaluminum, triisobutylaluminum, and trihexylaluminum.

The cocatalyst and promoter can be added to the supported vanadiumcomplex either before or during the polymerization reaction. They can beadded together or separately, simultaneously or sequentially. Thecocatalyst and promoter are preferably added separately as solutions inan inert solvent, such as isopentane, to the polymerization reaction atthe same time as the flow of the ethylene is initiated. The cocatalystis necessary to obtain any significant polymerization. The promoter, onthe other hand, can be considered a preferred option. About 5 to about500 moles, and preferably about 10 to about 40 moles, of cocatalyst canbe used per mole of vanadium catalyst, i.e., the reaction product of thevanadium compound and the electron donor.

The autoacceleration inhibitor can be a Diels-Alder adduct or atransition metal carbonyl with the proviso that the inhibitor is suchthat it will decompose when the catalyst reaches the autoaccelerationtemperature range. It is believed that the decomposition product thenreacts with the active sites on the catalyst to prevent autoaccelerationfrom occurring. The inhibitor is preferably stable until it reaches thedecomposition temperature range. The autoacceleration temperature range,e.g., for a high density polyethylene vanadium catalyst system is in therange of about 110° to about 125° C. The decomposition temperature rangeof the autoacceleration inhibitor, then, preferably begins at the lowerend of this range. While the inhibitor can be either dry mixed with thecatalyst or added to the reactor as a separate component, it preferablyresides in the catalyst particles, e.g., the inhibitor is impregnatedinto a silica support along with the catalyst precursor.

Diels-Alder adducts are described in Streitwieser et al, Introduction toOrganic Chemistry, 3rd edition, Macmillan, N.Y., 1985, pages 550 to 558.Those which are useful as autoacceleration inhibitors, in accordancewith this invention, can have about 4 to about 20 carbon atoms andpreferably have about 4 to about 10 carbon atoms. They can have one ortwo carbon to carbon unsaturated bonds and be either monocyclic orpolycyclic. Further, they can be substituted or unsubstitutedhydrocarbon compounds. Examples of suitable substituents are methyl,ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl,n-pentyl, -2-pentyl, -3-pentyl, neopentyl, n-hexyl, 2-hexyl and phenyl;examples of dienes, which can be used to make the adducts, are1,3-butadiene, 1,3-pentadiene, 2-methyl-1,3-butadiene (isoprene),1,3-hexadiene, 2,4-hexadiene, 2,3-dimethyl-1,3-butadiene,2,4-dimethyl-1,3-hexadiene, 2,5-dimethyl-2,4-hexadiene, cyclopentadiene,methylcyclopentadiene, 1,3-cyclohexadiene, 1,3-cycloheptadiene, and1,3-cyclooctadiene; and examples of monoenes or dienophiles, which canbe used to make the adducts, are sulfur dioxide, carbon monoxide,cyclopentadiene, vinyl acetate, acrylic acid, dimethylacetylenedicarboxylate, ethylene, methyl vinyl ketone, diethylacetylenedicarboxylate, acrolein, and methyl acrylate. Examples ofuseful Diels-Alder adducts are dicyclopentadiene, methylcyclopentadienedimer, butadiene sulfone, isoprene sulfone, and vinylene carbonate.

Autoacceleration inhibitor compounds also useful in the practice of thisinvention are transition metal carbonyls. The metal is generallyselected from Groups VIB, VIIB, and VIII of the periodic table.Transition metals of particular interest are chromium, molybdenum, iron,tungsten, ruthenium, osmium, rhenium, and manganese. The transitionmetal carbonyls can be inorganic or organic compounds. The organiccompounds can contain either unsubstituted or substituted aliphatic oraromatic organic groups provided that the substituents are inert to theparticular process in which the inhibitor is being used. Preferably, theorganic groups are limited to 2 to 20 carbon atoms, e.g., methyl, ethyl,propyl, isopropyl, butyl, isobutyl, pentyl, heptyl, phenyl, or benzyl.Examples of suitable transition metal carbonyl inhibitors are Cr(CO)₆ ;Mo(CO)₆ ; Fe(CO)₅ ; W(CO)₆ ; C₅ H₅ Fe(CO)₂ I; C₇ H₈ Mo(CO)₃ ; C₆ H₅ CO₂CH₃ Cr(CO)₃ ; C₆ H₅ NHCH₃ Cr(CO)₃ ; Fe₃ (CO)₁₂ ; Ru₃ (CO)₁₂ ; Os₃ (CO)₁₂; Re₂ (CO)₁₀ ; and Mn₂ (CO)₁₀.

Mixtures of Diels-Alder adducts and mixtures of transition metalcarbonyls can be used as well as mixtures of Diels-Alder adducts andmetal carbonyls.

The autoacceleration inhibitor is preferably used in a molar ratio ofinhibitor to transition metal in the transition metal catalyst in therange of about 0.1:1 to about 200:1 and preferably a molar ratio in therange of about 0.5:1 to about 100:1. The inhibitor can be (i) dry mixedwith an impregnated silica support; (ii) impregnated from a solutioninto a silica support, which has been impregnated with a catalystprecursor; (iii) slurried in an electron donor or other inert solventwith silica prior to the addition of the reaction product of vanadiumtrihalide and the same electron donor; or added to the reactorseparately. In all cases, the silica is preactivated by dehydrating withheat. Any of these routes is more effective than dry mixing theinhibitor with the silica supported vanadium catalyst. In any case, theinhibitors used in the preparation of subject catalyst should beessentially free of water. The inhibitors can also be chemicallyanchored to the support, i.e., a chemical bond is formed between theinhibitor and the support as opposed to a physical adsorption of theinhibitor on the surface of the support. In any of these procedures, thedecomposition temperature range of the inhibitor should be avoided.

Optionally, a modifier is included in the vanadium catalyst system andis impregnated into the catalyst support. The formula for the modifieris BX₃ or AlR.sub.(3-a) X_(a) wherein each R is an alkyl radical having1 to 14 carbon atoms; X is chlorine, bromine, or iodine; each R and Xare alike or different; and a is 0, 1, or 2. Preferred modifiers includealkylaluminum mono- and di- chlorides wherein each alkyl radical has 1to 6 carbon atoms, and boron trichloride. A particularly preferredmodifier is diethyl aluminum chloride. About 0.1 to about 10 moles, andpreferably about 0.2 to about 2.5 moles, of modifier are used per moleof electron donor. When the modifier is used it appears to be part ofthe vanadium trichloride/electron donor complex.

The ethylene polymerization or copolymerization can be conducted in thegas phase or liquid phase using conventional techniques such asfluidized bed, slurry, or solution processes. Solution and slurrypolymerizations are described in Stille, Introduction to PolymerChemistry, Wiley and Sons, N.Y., 1962, and fluidized bed processes inU.S. Pat. No. 4,482,687. A continuous, fluidized bed process ispreferred. Using this fluidized bed process, the vanadium complex, thecocatalyst, the promoter, the ethylene monomer, and any comonomers arecontinuously fed into the reactor and polyethylene product iscontinuously removed. The density of ethylene copolymer produced may bevaried over a wide range depending upon the amount of alpha-olefincomonomer added and upon the particular comonomer employed. The greaterthe mole percent of alpha-olefin, the lower the density. Thealpha-olefin can have 3 to 12 carbon atoms.

The fluidized bed polymerization is conducted at a temperature below thesintering temperature of the product. The normal operating temperatureis generally in the range of about 10° C. to about 115° C. Preferrednormal operating temperatures will vary depending upon the densitydesired. High density polyethylenes of greater than about 0.94 grams percubic centimeter (g/cc) are produced at normal operating temperatures ofabout 85° C. to about 115° C., and preferably about 90° C. to about 100°C. Low density polyethylenes ranging in density from about 0.91 to about0.94 g/cc are preferably produced at a normal operating temperature ofabout 75° C. to about 90° C. Very low density polyethylenes of less thanabout 0.91 g/cc are preferably produced at a normal operatingtemperature of about 10° C. to about 80° C. In the case of very lowdensity polyethylenes, it is necessary to dilute the reaction mixturewith a large quantity of diluent gas in order to prevent the formationof polymer agglomerates and sustain polymerization on a continuousbasis.

The fluidized bed reactor is typically operated at pressures of up toabout 1,000, and preferably about 50 to about 350, psig.

A chain transfer agent, such as hydrogen, can be used to terminate thepolymer chain. Usually the ratio of hydrogen employed to ethylene willvary between about 0.001 to about 2.0 moles of hydrogen per mole ofethylene.

The autoacceleration inhibitor acts to essentially curb autoaccelerationwhile not interfering with the high activity of the catalyst at normaloperating temperatures to any great extent.

The vanadium based catalyst, except for the autoacceleration inhibitor,and its preparation are closely related to the catalyst described inU.S. Pat. No. 4,508,842.

The patents and publications mentioned in this specification areincorporated by reference herein.

The invention is illustrated by the following examples:

EXAMPLES 1 to 21

A supported vanadium based catalyst is typically prepared as follows:silica gel is preactivated at a temperature in the range of about 250°C. to about 800 ° C. under a dry, inert gas such as nitrogen for about 8to about 16 hours to give a support essentially free of adsorbed waterand containing less than about 0.7 millimole per gram of silica ofsurface hydroxy groups. The silica is slurried in freshly distilledtetrahydrofuran (THF), under nitrogen. An amount of VCl₃ (THF)₃ is addedto give a loading of about 0.2 to about 0.6 millimole of vanadium pergram of support. The mixture is stirred for about 20 to about 40minutes, then excess THF is removed. If diethylaluminum chloride (DEAC)modification is desired, the DEAC is added after the excess THF isremoved. A solution of inhibitor in hexane is then added with additionalstirring, after which the solvent is removed to give a free flowingpowder.

In these examples, a VCl₃ (THF)₃ solution was added to a slurry ofpreactivated silica in THF and then dried at 45° C. to a free-flowingpowder. This is the catalyst precursor. It was then treated with DEAC asdescribed above. The result was a silica-supported VCl₃ (THF)₃ (DEAC)₁.5catalyst. Except for examples 1 and 8, an autoacceleration inhibitor wasadded by one of three different methods as follows:

A. added as a separated component to the reactor;

B. dry-mixed with the catalyst; or

C. co-impregnated with the catalyst precursor and DEAC into the silicasupport. This is accomplished by dissolving the inhibitor in hexane ormethylene chloride and mixing the catalyst with this solution for 30minutes. The solvent is then removed to give a free-flowing powder.

The catalyst, the inhibitor (according to methods A, B or C), atriethylaluminum (TEAL) cocatalyst, and a fluorotrichloromethanepromoter (except in example 7 where the promoter is1,1,1-trichloroethane) were added to a reactor containing 600milliliters of hexane. An amount of catalyst sufficient to give a chargeof 0.05 millimole of vanadium was used. Forty equivalents each ofcocatalyst and promoter were used per equivalent of vanadium.

Two runs of 30 minutes each were carried out for each example. One runwas effected at 85° C., which is within the normal operating range forthe catalyst system. In this case, the reactor was initially pressurizedwith ethylene and one psi of hydrogen for a total pressure of 160 psig.The other run was effected at 125° C., which is within theautoacceleration temperature range for the catalyst system. In this run,the cocatalyst and the ethylene were added when the reactor reaches atemperature of 120° C. The hydrogen was added at 60° C.

Variables and results are set forth in Tables II and III. Notes withrespect to the Examples and Tables

1. THF=tetrahydrofuran

2. DEAC=diethylaluminum chloride

3. Inhibitor=autoacceleration inhibitor

4. Inhibitor/V=mole ratio of inhibitor to vanadium.

5. Method of Incorporation=A, B, or C, as above.

6. The activity of the catalyst was measured in grams of polyethyleneper millimole of vanadium per hour per 100 psig of ethylene.

7. % Change=the difference in activity between control examples withoutinhibitors and examples with inhibitors. Examples 2 to 7 are compared toexample 1 and examples 9 to 21 are compared to example 8.

8. Examples 1 to 7 were performed by adding the catalyst, thecocatalyst, the promoter, and the inhibitor (examples 2 to 7) asseparate components directly to the reactor. In contrast, examples 8 to21 were carried out by first mixing together the catalyst, thecocatalyst, the promoter, and the inhibitor (examples 9 to 21) in asmall bottle, and then adding the mixture to the reactor.

9. The controls (no inhibitor) differ in that example 1 shows no majoractivity change in going from 85° C. to 125° C. whereas example 8 showsa nearly two-fold increase in activity from 85° C. to 125° C. Thisdifference in behavior is believed to result from the two differentaddition methods that were used (see Note 8).

                                      TABLE II                                    __________________________________________________________________________                                 Activity                                                              Method of       % Change                                                                            % Change                           Example                                                                            Inhibitor Inhibitor/V                                                                         Incorporation                                                                         85° C.                                                                     125° C.                                                                    85° C.                                                                       125° C.                     __________________________________________________________________________    1    --        --    --      1044                                                                              1077                                                                              --    --                                 2    dicyclopentadiene                                                                       20    A       1095                                                                              751 +5    -30                                3    dicyclopentadiene                                                                       40    A       1370                                                                              453 +31   -58                                4    dicyclopentadiene                                                                       160   A       1116                                                                              270 +7    -75                                5    butadiene sulfone                                                                       5     B       578 177 -45   -84                                6    isoprene sulfone                                                                        4     B       568 65  -46   -94                                7    vinylene carbonate                                                                      5     B       1470                                                                              668 +41   -38                                __________________________________________________________________________

                                      TABLE III                                   __________________________________________________________________________                                  Activity                                                              Method of       % Change                                                                            % Change                          Example                                                                            Inhibitor  Inhibitor/V                                                                         Incorporation                                                                         85° C.                                                                     125° C.                                                                    85° C.                                                                       125° C.                    __________________________________________________________________________    8    --         --    --      748 1473                                                                              --    --                                9    Cr(CO).sub.6                                                                             1     A       739 495 -1    -66                               10   Mo(CO).sub.6                                                                             0.5   A       713 511 -5    -65                               11   Mo(CO).sub.6                                                                             1     A       956 422 +28   -71                               12   Mo(CO).sub.6                                                                             2     A       741 328 -1    -78                               13   Mo(CO).sub.6                                                                             1     B       835 966 +12   -34                               14   Mo(CO).sub.6                                                                             1     C       910 934 +20   -37                               15   W(CO).sub.6                                                                              1     A       677 837 -10   -43                               16   Fe(CO).sub.5                                                                             1     A       766 405 +2    -73                               17   C.sub.5 H.sub.5 Fe(CO).sub.2 I                                                           1     A       430 417 -43   -72                               18   C.sub.7 H.sub.8 Mo(CO).sub.3                                                             1     A       704 372 -6    -75                               19   C.sub.7 H.sub.8 Mo(CO).sub.3                                                             1     C       733 439 -2    -70                               20   C.sub.6 H.sub.5 CO.sub.2 CH.sub.3 Cr(CO).sub.3                                           1     C       970 905 +30   -39                               21   C.sub.6 H.sub.5 NHCH.sub.3 Cr(CO).sub.3                                                  1     C       780 812 +4    -45                               __________________________________________________________________________

EXAMPLES 22 to 27

The solid catalyst described above was employed toothier with acocatalyst (triethylaluminum), a promoter (CHCl₃), and an inhibitor(dicyclopentadiene) to copolymerize ethylene and 1-hexene in a fluid bedreactor system similar to that described in U.S. Pat. No. 4,482,687.

In each polymerization, the solid catalyst component was continually fedto the polymerization reactor along with the cocatalyst, the promoter,and the inhibitor.

Hydrogen was added to the reactor as a chain transfer agent to controlthe molecular weight of the polymer produced. Nitrogen was also used tomaintain the total pressure at a set point.

Table IV below sets forth the catalyst composition and the reactionconditions that were employed. Table V presents two control experiments(examples 22 and 23), run without the inhibitor, which show the normalvariation of catalyst activity (vanadium in resin, parts per million).Examples 24 to 27 are experiments to ascertain the effect of temperatureon catalyst activity in the presence of the inhibitor.

The examples show that the inhibitor has a stabilizing effect within thenormal operating range of the catalyst system.

                                      TABLE IV                                    __________________________________________________________________________    Catalyst       Reaction Conditions                                            __________________________________________________________________________    Support: Silica gel                                                                          Temp. (°C.)                                                                            90 to 110                                      Precursor: VCl.sub.3 /THF                                                                    Total pressure  315 psia                                       Modifier: DEAC C.sub.2 H.sub.4 pressure                                                                      230 psia                                       Modifier/V Molar Ratio: 1.78                                                                 N.sub.2 pressure                                                                              80 psia                                        Cocatalyst: TEAL                                                                             H.sub.2 pressure                                                                              3.7 to 5.8 psia                                Promoter: CHCl.sub.3                                                                         Comonomer       1-hexene                                       Al/V Molar Ratio: 24                                                                         Comonomer/C.sub.2 H.sub.4 (molar ratio)                                                       0.004 to 0.017                                 Promoter/V Molar Ratio: 24                                                                   H.sub.2 /C.sub.2 H.sub.4 (molar ratio)                                                        0.016 to 0.025                                                Residence Time  4 hr                                                          Inhibitor       Dicyclopentadiene                                             Inhibitor/V (molar ratio)                                                                     5.0 to 11.0                                    __________________________________________________________________________

                  TABLE V                                                         ______________________________________                                        Ex-                         Vanadium                                          am-  Dicyclopentadiene/V                                                                          Temp.   in Resin                                          ple  (molar ratio)  (°C.)                                                                          (ppm)   Comments                                  ______________________________________                                        22   0              90      7.4     --                                        23   0              105     2.5     --                                        24   8.0            90      6.5     More stable                                                                   operation                                 25   7.8            100     6.0     More stable                                                                   operation                                 26   11.2           110     6.0     More stable                                                                   operation                                 27   5.0            110     6.9     More stable                                                                   operation                                 ______________________________________                                    

We claim:
 1. A transition metal catalyst system comprising a transitionmetal catalyst and an autoacceleration inhibitor, which (i) at about thetemperature at which the catalyst system autoaccelerates, decomposesinto a poison for the catalyst system; (ii) is present in the catalystsystem in an amount sufficient to provide the quantity of poisonrequired to inhibit the catalyst system at the autoaccelerationtemperature; and (iii) is either essentially inert at the normaloperating temperature of the catalyst system or will cause substantiallyless inhibition of the catalyst system at the normal operatingtemperature than at the autoacceleration temperature.
 2. The transitionmetal catalyst system defined in claim 1 wherein the inhibitor is aDiels-Alder adduct.
 3. The transition metal catalyst system defined inclaim 1 wherein the inhibitor is a transition metal carbonyl.
 4. Thetransition metal catalyst system defined in claim 2 wherein theDiels-Alder adduct has about 4 to about 20 carbon atoms.
 5. Thetransition metal catalyst system defined in claim 4 wherein theDiels-Alder adduct is monocyclic or polycyclic.
 6. The transition metalcatalyst system defined in claim 2 wherein the Diels-Alder adduct is asulfone.
 7. The transition metal catalyst system defined in claim 2wherein the Diels-Alder adduct is a carbonate.
 8. The transition metalcatalyst system defined in claim 5 wherein the Diels-Alder adduct ispolycyclic.
 9. The transition metal catalyst system defined in claim 8wherein the Diels-Alder adduct is dicyclopentadiene.
 10. The transitionmetal catalyst system defined in claim 3 wherein the transition metal ofthe transition metal carbonyl is molybdenum, chromium, tungsten, oriron.
 11. The transition metal catalyst system defined in claim 3wherein the transition metal carbonyl contains, in addition to thecarbonyl groups, unsubstituted or substituted organic groups having 2 to20 carbon atoms with the proviso that the substituent is inert insofaras the process in which the inhibitor is to be used is concerned. 12.The transition metal catalyst system defined in claim 1 wherein theinhibitor is present in a molar ratio of inhibitor to transition metalin the range of about 0.1:1 to about 200:1.
 13. The transition metalcatalyst system defined in claim 12 wherein the inhibitor is present ina molar ratio of inhibitor to transition metal in the range of about0.5:1 to about 100:1.
 14. The transition metal catalyst system definedin claim 1 wherein the transition metal catalyst is particulate and theinhibitor resides in substantially all of the transition metal catalystparticles.
 15. In a transition metal catalyst system, the improvementcomprising including in the catalyst system an autoaccelerationinhibitor, which (i) at about the temperature at which the catalystsystem autoaccelerates, decomposes into a poison for the catalystsystem; (ii) is present in the catalyst system in an amount sufficientto provide the quantity of poison required to inhibit the catalystsystem at the autoacceleration temperature; and (iii) is eitheressentially inert at the normal operating temperature of the catalystsystem or will cause substantially less inhibition of the catalystsystem at the normal operating temperature than at the autoaccelerationtemperature.
 16. A vanadium catalyst composition comprising:(i) thereaction product of a vanadium compound and an electron donor, which isa liquid, organic Lewis base in which the vanadium compound is soluble;(ii) a silica support into which component (i) is impregnated; (iii) ahalocarbon promoter; (iv) a hydrocarbyl aluminum cocatalyst; and (v) asan autoacceleration inhibitor, a Diels-Alder adduct or a transitionmetal carbonyl,with the proviso that the inhibitor is such that it willdecompose when the catalyst reaches its autoacceleration temperature.17. The vanadium catalyst composition defined in claim 16 wherein theLewis base is an alkyl ester of an aliphatic or an aromatic carboxylicacid, an aliphatic ketone, an aliphatic amine, an aliphatic alcohol, analkyl or cycloalkyl ether, or a mixture thereof.
 18. The vanadiumcatalyst composition defined in claim 16 additionally comprising:(vi) amodifier having the formula BX₃ or AlR.sub.(3-a) X_(a) wherein each R isan alkyl radical having 1 to 14 carbon atoms; X is chlorine, bromine, oriodine; each R and X are alike or different; and a is 0, 1, or
 2. 19.The vanadium catalyst composition defined in claim 16 wherein theinhibitor is a Diels-Alder adduct.
 20. The vanadium catalyst compositiondefined in claim 16 wherein the inhibitor is a transition metalcarbonyl.
 21. The vanadium catalyst composition defined in claim 19wherein the Diels-Alder adduct has about 4 to about 20 carbon atoms. 22.The vanadium catalyst composition defined in claim 19 wherein theDiels-Alder adduct is monocyclic or polycyclic.
 23. The vanadiumcatalyst composition defined in claim 16 wherein the inhibitor ispresent in a molar ratio of inhibitor to vanadium in the range of about0.1:1 to about 200:1.
 24. The vanadium catalyst composition defined inclaim 23 wherein the inhibitor is present in a molar ratio of inhibitorto vanadium in the range of about 0.5:1 to about 100:1.
 25. The vanadiumcatalyst composition defined in claim 18 wherein the cocatalyst istriisobutyl aluminum.
 26. The vanadium catalyst composition defined inclaim 18 where the cocatalyst is triethylaluminum.
 27. The vanadiumcatalyst composition defined in claim 18 wherein the cocatalyst istrihexylaluminum.
 28. The vanadium catalyst composition defined in claim18 wherein the promoter is CHCl₃, CH₃ CCl₃, or CFCl₃.
 29. The vanadiumcatalyst composition defined in claim 20 wherein the transition metal ofthe inhibitor is selected from Groups VIB, VIIB, and VIII of theperiodic table.
 30. The vanadium catalyst composition defined in claim29 wherein the transition metal of the inhibitor is chromium,molybdenum, tungsten, or iron.
 31. The vanadium catalyst compositiondefined in claim 28 wherein the transition metal carbonyl is Cr(CO)₆ ;Mo(CO)₆ ; Fe(CO)₅ ; W(CO)₆ ; C₅ H₅ Fe(CO)₂ I; C₇ H₈ Mo(CO)₃ ; C₆ H₅ CO₂CH₃ Cr(CO)₃ ; C₆ H₅ NHCH₃ Cr(CO)₃ ; Fe₃ (CO)₁₂ ; Ru₃ (CO)₁₂ ; Os₃ (CO)₁₂; Re₂ (CO)₁₀ ; or Mn₂ (CO)₁₀.
 32. The vanadium catalyst compositiondefined in claim 18 wherein the modifier is diethylaluminum chloride.33. The vanadium catalyst composition defined in claim 18 wherein themodifier is present in an amount of about 0.1 to about 10 moles per moleof electron donor.
 34. The vanadium catalyst composition defined inclaim 32 wherein the modifier is present in an amount of about 0.2 toabout 2.5 moles per mole of electron donor.
 35. The vanadium catalystcomposition defined in claim 16 wherein the inhibitor resides in theimpregnated support.